This invention relates to an apparatus for staining microscope slides and more particularly to an apparatus for maintaining the temperature of a reagent film on a microscope slide at an elevated temperature within a predetermined range.
In the microscopic examination of certain material, particularly cellular materials such as blood, tissue, or the like, a specimen of the material is placed on a transparent microscope slide. Thereafter, the material is stained by contacting it with solutions which stain or dye only certain constituents of the cell to provide a contrast which facilitates visual examination. Microscope slides are presently being stained by both manual and automated techniques. To manually stain a slide it is submersed successively in bulk reagents, each reagent remaining in contact with the specimen for a predetermined time before the specimen is submersed into a succeeding reagent solution. The slide is then rinsed and dried.
Because of the excessive amount of time required for hand staining and due to the fact that contamination can be caused by submersing many slides in the same container of solution, mechanized means are being increasingly employed for staining microscope slides. This type of apparatus conveys the slides through a plurality of stations where the staining reagents are automatically applied to the specimen. For example, U.S. Pat. No. 3,431,886 issued to J. B. McCormick et al. teaches an apparatus for conveying slides in a horizontal position over a flat liquid-applying surface and injecting a treating liquid into the space between the slide and surface. The slides are then moved into a vertical position for draining and drying. Another automatic staining apparatus is disclosed in U.S. Pat. No. 3,853,092 issued to L. G. Amos et al. This apparatus conveys the microscope slides in a circular path and automatically dispenses a metered amount of various reagents on the upper surface of the slides. The apparatus also imparts a nutating motion to the slide to effect uniform wetting of the top surface thereof by each reagent and by the rinse. The slides are thereafter moved to a near vertical position for draining and drying.
By controlling the time during which the specimen is subjected to each reagent and by carefully metering the amount of reagents applied, the stained specimens exhibit sufficient contrast for visual analysis. For example, laboratory technicians can perform what is referred to as a white blood cell differential by counting the leukocytes on a stained blood smear. Because of the amount of time required for a technician to analyze a biological specimen and due to the increasing number of analyses being performed, automation of tests such as the white blood cell differential is inevitable. A thesis by J. W. Bacus, "An Automated Classification of the Peripheral Leukocytes by Means of Digital Image Processing", University of Illinois, Chicago, 1971, describes one automated system. A system for automatically scanning and digitizing the count of leukocytes on a stained smear is disclosed in copending application Ser. No. 353,004 entitled "Image Scanning Converter for Automated Slide Analyzer" filed by D. A. Cotter on Apr. 20, 1973 now U.S. Pat. No. 3,883,852 issued May 13, 1975.
The accuracy with which automated slide analysis can be performed depends upon the reproducibility of the slide staining process. Each blood film, for example, should be stained so that the optical density of a given type of nucleus substantially achieves a specified value. Furthermore, the staining process should provide optimal contrast between the cell nucleus and cytoplasm.